The present invention relates to a method for simultaneous recrystallisation and doping of semiconductor layers, in particular for the production of crystalline silicon thin layer solar cells and semiconductor layer systems produced according to this method, in particular crystalline silicon thin layer solar cells.
The production of thin, doped semiconductor layers or layer systems for electronics and photovoltaics is implemented at present in the most varied of ways. In general, the aim is to produce sandwich-like layer structures comprising differently doped partial layers. Typically, a plurality of process steps is thereby used, with which such a layer structure is constructed sequentially. The construction takes place either by growing partial layers (deposition, epitaxy) or by introducing a dopant (for example by diffusion or implantation). The methods are typically characterised in that a plurality of implanting processes or deposition processes is required in order to produce a plurality of differently doped layers. The exceptions are so-called co-diffusion processes in which differently doped layers are produced simultaneously from different dopant sources.
The present invention relates to semiconductor layer structures in which the semiconductor is recrystallised after a deposition step again via the liquid phase in order for example to change the crystal structure. Such an application is provided for example in “Silicon on Insulator” (SOI) technology or in the field of crystalline silicon thin layer solar cells. The invention is explained subsequently by way of example in particular with reference to the latter system.
Crystalline silicon thin layer solar cells are produced at present by different methods. One of these methods from prior art comprises the following process steps:                1. Production of a substrate.        2. Deposition of a conductive intermediate layer.        3. Deposition of a seed layer which is normally enriched with dopant which causes an n or p conductivity in the seed layer.        4. Application of a “capping” layer by deposition or thermal oxidation.        5. Heating and recrystallisation of the seed layer.        6. Removal of the capping layer.        7. Deposition of the photovoltaically active absorber layer.        8. Production of the pn transition by introducing a dopant into the active absorber layer.        9. Application of the metallisation.        
The seed layer thereby serves both for the purpose of forming crystallisation seeds for the epitaxial deposition of the absorber and for forming a so-called “back surface field” (BSF) in order to reduce charge carrier recombinations. The seed layer is normally highly doped for this purpose.
Starting from the state of the art, it is the object of the present invention to make the separate deposition of the photovoltaically active absorber layer superfluous without requiring to cut back on the functionality of the basic construction, in particular the presence of the BSF layer.